1. Field of the Invention
The present invention relates to a lens driver which moves a lens holder in an optical axis direction relative to a supporter.
2. Description of the Related Art
A lens driver, which moves a holder for a zooming lens and a focusing lens in an optical axis direction relative to a supporter movably supporting the holder, is used in an imaging device such as a video camera or a digital still camera having an autofocus function and power zoom function. The lens driver is provided with a driver which moves the holder relative to the supporter and a position detector which detects the position of the moved holder (lens held in holder).
Regarding the position detector, it is considered to provide in the holder a position-detecting magnet, which is magnetized in the optical axis direction, and a magnetism-detecting element (magnetic sensor) in a position in the supporter, which faces the position-detecting magnet in the optical axis direction (for example, refer to Patent Document 1, JP 4247622B). In this position detector, upon the movement of the holder in the optical direction relative to the supporter, the interval between the position-detecting magnet and the magnetism-detecting element is changed according to the position, so that the intensity of the magnetic field formed by the position-detecting magnet is changed according to the interval in the magnetism-detecting element. Therefore, an unambiguous relationship between the output voltage value from the magnetism-detecting element and the positional relationship of the supporter and the holder can be obtained. For this reason, in the position detector, the position of the holder can be detected based on the output voltage value of the magnetism-detecting element regardless of the position of the holder relative to the supporter, thus, the position of the holder can be immediately detected.
However, in the above-described position detector (lens driver), if a distance from the position-detecting magnet exceeds a predetermined length, intensity of a magnetic field formed by the position-detecting magnet hardly changes relative to a change in a position, so that the moving range of the holder relative to the supporter is limited. In this case, in the above-described position detector (lens driver), it is considered to provide two magnetism-detecting elements to sandwich the position-detecting magnet in the optical axis direction. However, such a configuration is only to double the moving range compared to a configuration having a single magnetism-detecting element, and the moving range of the holder relative to the supporter is also limited. In addition, in the above-described position detector (lens driver), it is necessary to provide a position-detecting magnet dedicated for detecting a position of a holder.